1. Field of the Invention
The present invention relates to an acoustic apparatus for generating an acoustic wave obtained by synthesizing resonant acoustic waves radiated from a plurality of resonators having different resonance frequencies.
2. Description of the Prior Art
As a conventional acoustic apparatus of this type, a speaker system with a port disclosed in U.S. Pat. No. 4,549,631 is known. FIG. 12 shows an arrangement when the speaker system in U.S. Pat. No. 4,549,631 is put into a practical application. In the speaker system shown in FIG. 12, an internal space of a cabinet 1 having a known rectangular section is partitioned into two chambers 1a and 1b by a partition plate 2. Opening ports 3a and 3b are disposed on the outer walls of the chambers 1a and 1b, respectively, so that the chamber 1a and the opening port 3a and the chamber 1b and the opening port 3b form two Helmholtz resonators. In these Helmholtz resonators, resonance frequencies defined by the air springs in the chambers 1a and 1b as closed cavities and air masses of sound paths 4a and 4b of the opening ports 3a and 3b as acoustic mass means are respectively set to be f.sub.1 and f.sub.2 (f.sub.1 &lt;f.sub.2). An opening 2a is formed in the partition plate 2, and a vibrator (dynamic speaker unit) 5 is mounted in this opening 2a. A diaphragm 6 of the vibrator 5 is mounted to close the opening 2a. The front surface of the diaphragm 6 opposes the chamber 1a, and its rear surface opposes the chamber 1b.
Since this speaker system drIves the resonators by the front and rear surfaces, the directions of resonance radiation from the two resonators are opposite to each other. For this reason, in a system arrangement, acoustic radiation spaces for the two, i.e., front and rear surfaces must be taken into consideration, and this speaker system has no single-sidedness as in normal speaker system. Although directivity is approximate to a nondirectional characteristic in a bass range, a user experiences sounds produced from two different positions at a normal audible distance. As a result, a sound source position becomes unclear, i.e., a sound image is dispersed.
Note that in a speaker system shown in FIG. 1 of U.S. Pat. No. 4,549,631, since opening ports are disposed on a single surface of a cabinet, the first problem, i.e., no single-sidedness in the system arrangement can be solved. However, since the opening ports are disposed to be horizontally or vertically separate from each other with respect to the vibrator 5, the second problem, i.e., dispersion of a sound image is left unsolved. A similar speaker system is also shown in the European Patent Publication (A1) No. 0125625.